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The modern technique for balloon pulmonary valvuloplasty (BPV) was described in 1982 (1). Numerous reports over the past 25+ years have shown that BPV uniformly relieves pulmonary stenosis in patients with the typical isolated pulmonary valve abnormality. The remarkable safety and efficacy of this procedure really opened the door to the development of the specialty of interventional catheterization for congenital heart disease. It has also long been recognized that patients develop some degree of pulmonary regurgitation (PR) after BPV, but the prevalence, degree, and consequences of the pulmonary regurgitation are far less well elucidated. In this issue of the Journal, Harrild et al. (2) from Boston report some of the most detailed data to date on these issues.

The good news from the Boston study is that the typical degree of PR following BPV is remarkably mild. In a somewhat select group of patients, median PR fraction was only 10%, and median right ventricular (RV) volume was in the normal range (z-score = 1.5) at a median of 13.1 years post-BPV. This study excluded patients with significant residual pulmonary stenosis, and presumably, any patients who may have undergone pulmonary valve replacement prior to the study. The bad news is that PR can sometimes be severe. The present study found that 11% (4 of 35) of BPV patients followed in Boston had an RV volume index z-score ≥ 4 and an absolute RV volume index >140 ml/m2.

Not too surprisingly, in the Boston study, the use of an oversized balloon for the BPV was associated with a higher probability of more severe PR as measured by PR fraction. Berman et al. (3), were among the first to report the need for pulmonary valve replacement in some patients after BPV (3). They reported in 1999 that 6% of their patients had PR severe enough to consider pulmonary valve replacement on clinical and qualitative echocardiographic grounds, but did not have quantitative data on the degree of PR or RV volumes. They advised caution in the use of oversized balloons, especially in neonates and infants with severe stenosis. The Boston group similarly found that caution is warranted when considering a balloon to annulus ratio (BAR) >1.4. Inspection of the Boston data and graphs, however, shows that the relationship between BAR and degree of PR for any individual patient was not particularly strong. A number of patients with BAR <1.4 had PR fraction >20% (a percentage that is commonly used to denote the boundary between mild and moderate). Interestingly, there were also a number of patients with BAR as high as 1.9, but with relatively mild PR fraction. As Harrild et al. (2) point out, a target BAR of 1.2 to 1.4 seems best, but adherence to this target will not guarantee minimal PR. The Boston study was not designed to address the question of how to proceed if a patient still has a significant post-dilation gradient after BPV with a balloon in the target range. The best approach to these patients needs further study.

Much of the cardiac magnetic resonance (CMR) data from the Boston study is not unexpected. For instance, one would expect a close correlation between PR volume (indexed for body size) and PR fraction. There may be some debate about whether PR fraction or PR volume is a better index to follow, but they are related (4). It is not too surprising that PR fraction was not related to duration between valvuloplasty and a single CMR study. The degree of PR at any 1 point in time for an individual patient is more likely related to the underlying anatomy and the technical aspects of the valvuloplasty (such as BAR). The Boston study was not designed to study how PR changes over time, but it would be interesting to know more about the “natural history” of PR progression following BPV. Clinically, PR is not very evident in the first months after BPV (perhaps because of RV hypertrophy and low compliance). It is not well known whether the PR will reach a certain level and remain stable, or progress relentlessly with time. The study also found that higher PR fraction is correlated with younger age at BPV. The study did not find that higher RV pressure (and intuitively a more abnormal valve) was related to late PR fraction. The study population spans a wide age range (1 day to 27 years) so RV:systemic pressure ratio might have given a better indication of relative severity of stenosis. It is not clear whether the best strategy to avoid late PR may be to wait until an asymptomatic patient with moderate stenosis is older before performing elective BPV.

In my view, the most uncertain conclusions from the paper by Harrild et al. (2) involve the relationship of PR to exercise performance. Exercise capacity is determined by a large number of factors, including inherent genetic differences between individuals, conditioning, motivation, method of testing, and function of the cardiovascular and respiratory systems. Although some of the technical factors concerning repeatability are well controlled because the studies were done at a single center, there is no matched control group and thus no good idea of the variability that might be seen in a well-matched normal population. Some index of baseline physical activity might be especially important to consider since sedentary lifestyle can have a significant effect on performance, and tends to be more common in patients with a diagnosis of congenital heart disease (5). In the author's analysis, if a patient did not achieve 85% of a predicted value (determined from a different study), this was considered abnormal (6). Certainly, this is a typical strategy for clinical testing, but doesn't help us to understand how many children in a typical classroom might also not achieve the 85% predicted mark. The authors note that there was no linear correlation between PR fraction and exercise capacity. Indeed, inspection of the figures shows that the patient with the highest regurgitant fraction had a peak Vo2 of 100% predicted, and at least 5 patients with peak Vo2 <85% predicted had very little PR (PR fractions <15%). The authors chose the 15% regurgitation fraction as an apparent indicator of significant regurgitation only after evaluating receiver-operator curves. Even using this approach, and grouping all levels of regurgitation >15% together, the analysis showed group differences of 96% predicted compared with 85% predicted to be significantly different only at the p = 0.03 level. Peak work using this approach was not significantly different between the groups with PR fraction less than 15% compared with those with PR fraction more than 15%.

The study by Harrild et al. (2) certainly does add to our body of knowledge regarding the effects of relatively isolated PR on measures of ventricular function and right ventricular size. The authors are to be congratulated for prospectively enrolling 40 (mostly) pediatric research patients to undergo CMR and metabolic exercise studies. The number of patients, however, is still quite small, and more data are needed to better understand how PR interacts with other factors to affect exercise tolerance (and ultimately long-term lifestyle and lifespan). In the not-too-distant future, percutaneous pulmonary valve replacement may be much more widely available. It appears that few patients after BPV will develop PR significant enough to meet the current criteria for surgical pulmonary valve replacement after repair of tetralogy of Fallot (RV end-diastolic volume index approximately >150/m2). In time, however, there may be a natural tendency to consider percutaneous pulmonary valve replacement with less stringent criteria. More studies like the Harrild et al. (2) study are needed in patients with isolated pulmonary stenosis before we should begin to consider early valve replacement as a means to alter or preserve exercise capacity.

Footnotes

↵⁎ Editorials published in the Journal of the American College of Cardiology reflect the views of the authors and do not necessarily represent the views of JACC or the American College of Cardiology.

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